Wire bonders are used in semiconductor assembly and packaging to make electrical connections between bond pads of electronic components. During wire-bonding of semiconductor devices, it is common to utilize a wire clamp to feed wire from a roll of bonding wire towards a bonding site, and to control and manipulate the wire. The wire is fed to a bonding tool, such as a tip of a capillary attached to a horn. An ultrasonic transducer is in turn coupled to the horn for generating ultrasonic bonding energy to bond the wire at the tip of the capillary.
The wire clamp is opened to allow wire to feed through during threading of the wire through a capillary and thereafter is closed to grip and control the wire. The wire clamp is also used to hold the wire in position during the making of first and second bonds on the electronic components. The clamp is further commonly used to enable looping of a length of bonding wire between electrical contact points on the electronic components, and/or to pull wires from bonds after the bonds have been made.
The wire clamp typically comprises a movable arm or member, and a fixed arm or member. The movable arm is opened and closed by a solenoid or a linear motor, and is usually urged towards the fixed arm by a spring or the motor. The bonding wire is very fine, often to the order of 1 mil or less. Thus the wire is easily broken if it is subjected to excessive force. It is important that a gap between the movable and fixed arms is sufficient for the wire to pass through, and yet not be so large as compared to the size of the wire when opened so that the clamping force cannot be easily or reliably controlled.
FIG. 1 is a plan view of a wire clamp 100 of the prior art. The wire clamp 100 generally comprises a fixed clamping arm 102 and a movable clamping arm 104. The movable clamping arm 104 is movable relative to the fixed clamping arm 102 about a pivot 106. A wire clamp motor, such as a linear motor 108, is used to drive the movement of the movable clamping arm 104. An opening stopper 110 is located at an extreme position of the movable clamping arm 104 to limit the opening motion of the movable clamping arm 104 and to define a clamp gap 112.
The clamp gap 112 located at the tips of the fixed and movable clamping arms 102, 104 for receiving bonding wire. To control the size of the clamp gap 112, the opening stopper 110 is adjustable to fix the maximum opening position of the movable clamping arm 104. A problem with this design is that the movable clamping arm 104 is configured to hit the opening stopper 110 when opening the wire clamp 100 in order to limit further movement of the movable clamping arm 104. Thus, an impact force is experienced by the wire clamp structure that excites the structure and causes structural vibration. Such unwanted vibration may affect clamping accuracy, and result in greater wear and tear of the apparatus.
Moreover, since the diameter of modern-day bonding wires is generally small, it is difficult to manually adjust the position of the opening stopper 110 to control the size of the clamp gap 112. Therefore, a jig has to be used to set the clamp gap 112, using apparatus such as that described in U.S. Pat. No. 6,948,387 entitled “Clamp Calibration Apparatus and Method”. This is time-consuming and has to be done every time the clamp gap needs to be changed for different wire diameters.
An example of another prior art method to control the clamp gap is disclosed in Japanese patent publication number JP 6-244234 entitled “Wire Bonder”. It uses a first spring member to control the closed position of a movable arm and a second spring member to control the open position of the movable arm. When the movable arm is in the open position, a motor force for actuating the movable arm is less than a preload force of the second spring member resisting the opening of the movable arm, so that a maximum opening position is defined. To close the movable clamper, the motor force is increased to overcome the preload force so that the second spring member is flexed. In this way, the disclosure seeks to minimize the clamp gap and also the impact force to avoid damage to the wire during wire bonding. Nonetheless, it still uses stopper in the form of a screw (item 32 in Drawing 2 therein) to limit the open position of the movable clamper. The position of the screw stopper will still have to be manually adjusted to fix the clamp gap size. The design of the wire clamp is also more complex and requires more parts, which may reduce reliability.